The present invention relates to a novel production method of tris(pentafluorophenyl)borane using pentafluorobenzene as a raw material. Tris(pentafluorophenyl)borane obtainable according to the invention is a very useful substance as a cocatalyst for the cationic complex polymerization or an intermediate of N,N-dimethylanilinium tetrakis(pentafluorophenyl)borate etc., which is useful similarly as a cocatalyst for the cationic complex polymerization.
In recent years, scientific literatures or patents dealing with the polymerization reaction using these compounds and organometallic complexes have increased remarkably. For example, J. Am. Chem. Soc., 113, 3626 (1991), Macromol. Chem. Rapid Commun., 2, p. p. 663-667 (1991) and the like are available. However, for the production of tris(pentafluorophenyl)borane, relatively expensive pentafluorobromobenzene has been used conventionally as a starting substance for the source of pentafluorophenyl group.
The method was that pentafluorobromobenzene was submitted to the bromine-metal exchange reaction at low temperature of -70.degree. C. using organometallic compounds such as butyllithium to generate pentafluorophenyllithium (J. Org. Chem., 29, 2385 (1964), J. Org. Chem., 31, 4229 (1966) and Synthesis of Fluoroorganic Compounds, p. 190, Springer-Verlag (1985)), which was then reacted with boron trichloride, boron trifluoride, or the like as a starting raw material of the source of boron, or that pentafluorobromobenzene was reacted with magnesium to generate a Grignard reagent like pentafluorophenylmagnesium bromide (J. Chem. Soc., 166 (1959), Z. Naturforschg., 20b, 5 (1965), Synthesis of Fluoroorganic Compounds, p. 141, Springer-Verlag (1985), which was then reacted with boron trichloride similarly as a starting raw material of the source of boron, thereby performing the production of tris(pentafluorophenyl)borane (J. Organometallic Chem., 2, 245-250 (1964).
Pentafluorobromobenzene is obtained by brominating pentafluorobenzene. If it is possible to directly produce tris(pentafluorophenyl)borane from pentafluorobenzene, then the production processes can be reduced by one process, leading to easy availability and also decreased price of a starting raw material.
In view of the said situation, the inventors investigated extensively on a synthetic method without using relatively expensive bromopentafluorobenzene as a starting raw material by changing the use of bromopentafluorobenzene to that of pentafluorobenzene as a starting substance for the production of tris(pentafluorophenyl)borane and eliminating the brominating process of pentafluorobenzene, leading to the invention.